Dividing the night in three parts

Zubayd ibn al-Haarith would divide the night in three parts: a part for himself, a part for his son, and a part for his other son ‘Abdur-Rahmaan. So he would pray [the night prayer], then say to one of them: ‘wake up [and pray]’, and if he was overcome with laziness, he would pray his part. He would then say to the other [son]: ‘wake up [and pray]’, and if he too was overcome with laziness, he would then [also] pray his part; [and with that] he would [end up] pray[ing] the entire night.